There has been a tremendous surge in the development of wireless communications systems to meet the growing need of individuals and business to communicate information without being tethered to a wire or cable. The development of wireless communications systems has prompted the development of a wide variety of RF devices for use in such systems. The testing and characterization of RF devices has been a major factor in their development. In the past, such testing has been carried out by applying an unmodulated RF earlier to the device and then receiving the response generated by the device upon receipt of the carrier. The operating characteristics of the device are assessed in accordance with the phase and magnitude of the response signal, as compared to the phase and magnitude of the input carrier.
RF testing in the manner described above incurs the disadvantage that the carrier applied to the device as the test stimulus often does not have the same characteristics as the signals supplied to the device under normal operating conditions. Modern radio systems typically employ digital modulation. Thus, the test results obtained by the use of an analog RF carrier as the test stimulus usually correlate poorly with the actual performance of the device under normal operating conditions, especially for non-linear devices.
Thus, there is a need for a technique for testing an RF device that more accurately assesses the characteristics of the device under normal operating conditions.